1. Field
The present application relates to wireless local area networks, and, more particularly, to voice quality measurement for Voice over Internet Protocol (VoIP) in a wireless local area network.
2. Description of the Related Art
Traditionally, the public switched telephone network (PSTN) has been used for telecommunications. In general, users place calls on the PSTN using a telephone that establishes an electrical connection with a local telephone office (a central office). The central office responds with a dial tone. The user then dials a telephone number identifying the destination of the call. A network of switching systems then connects the call between the caller and the destination.
In conventional telephony, voice quality is typically measured by the Mean Opinion Score (MOS score) standardized by the International Telecommunications Union (ITU). The MOS score is subjectively determined by the customer user experience and is defined in the ITU-T Recommendation G.107. The MOS score has a range of 0-5, with 4.5 generally considered a good quality voice sound.
The MOS score is related to an objective Rating Value (R-Value), which combines various transmission parameters relevant for the considered connection. The R-Value can be determined by analyzing the received voice data for a variety of parameters, such as latency, time delay, jitter, variation in the time delay, burst rate, loss rate, etc. The R-Value has a range of 0-100, with 90 considered a good quality voice signal. The ITU standardized equation for the R-Value is:R=R0−Is−Id−Ie-eƒƒ+A. R0 is the signal-to-noise ratio. Is is the signal impairment. Id is the delay impairments. Ie-eff is the effective equipment impairment. A is the advantage factor.
A recent advancement of telephony is the development VoIP. In VoIP, calls are carried on computer networks in addition to or instead of on the PSTN. The analog voice signals are converted to digital signals in data clusters called wireless frames. The wireless frames contain information as to where the data should be delivered. Instead of a telephone number, the voice data is sent to a specific IP address.
VoIP can be implemented on a wired local area network and/or a wireless local area network. When VoIP is implemented on a wired local area network, voice quality can be measured by examining the frames that carry the VoIP data. In particular, an R-Value is typically determined by examining the Real-time Transport Protocol (RTP) fields in the frames. However, when VoIP is implemented on a wireless local area network, particularly one operating in accordance with the IEEE 802.11 standard, an R-Value cannot be determined by examining the RTP field in the wireless frames because, except for header information, the wireless frames are encrypted.